Determining the Location of Metallic Needle from MR Images Distorted by Susceptibility Difference

ABSTRACT

PURPOSE: To calculate the appearance of the image distortion from metallic artifacts and to determine the location of a metallic needle from a distorted MR image. MATERIALS AND METHODS: To examine metal artifacts, an infinite metal cylinder in a strong magnetic field are assumed. The cylinder's axis leaned toward the magnetic field along some arbitrary angle. The Laplace equation for this situation was solved to investigate the magnetic field distortion, and the simulation was performed to evaluation the image artifact caused by both readout and slice-selection gradient field. Using the result of the calculation, the exact locations of the metal cylinder were calculated from acquired images. RESULTS: The distances between the center and the folded point are measured from images and calculated. Percentage errors between the measured and calculated distance were less than 5%, except for one case. CONCLUSION: The simulation was successfully performed when the metal cylinder was skewed at an arbitrary tilted angle relative to the main magnetic field. This method will make it possible to monitor and guide both biopsy and surgery with real time MRI.